1. Field of the Invention
The present invention relates to a copying machine having at least one cassette removably inserted therein for accommodating copy sheets, and more particularly, to the control of such a copying machine.
2. Description of the Prior Art
Generally with copying machines, such as electrophotographic copying machines, which are equipped with an automatic paper feeder, sequential control for paper feeding and various other operations is executed when the machine is initiated into a copying operation (i.e., when the print switch is turned on). At this time, the advance of the copy paper fed out is checked by the use of various switching devices for detecting the presence or absence of the copy paper in the transport path of the paper. Generally, a timer is brought into operation to time the transport time of the copy paper to detect a jam when the copy paper has not reached or completely passed by a switch device within a predetermined period of time set on the timer. The jam detecting function is also performed under the sequential control.
On the other hand, copying machines provided with an automatic paper feeder also have paper absence detecting means for determining whether the copy paper stored in a paper accommodating portion has been exhausted in order to prevent the start of a copying operation. The copy machine is controlled to initiate its copying operation in accordance with a start signal for starting the copying operation when the paper accommodating portion is not empty.
The copying machines having a cassette removably inserted in the main body for accommodating sheet paper include those which require some initial period of time in which to start feeding the sheet paper after a copying operation start signal has been emitted. These copying machines generally have the function of checking the stock of paper upon the emission of a start signal, but the paper stock is not subsequently checked at the moment when a sheet of paper is to be actually fed out. Consequently, if the user recognizes, immediately after depressing the print switch, that the sheet paper of a desired size or kind is not installed for use and withdraws the paper accommodating cassette, the machine nevertheless starts its copying operation, executing sequential control including jam detection because the presence of the paper has been detected upon the initial depression of the print switch. It is therefore likely that the jam detecting means will function to stop the copying operation and display a jam signal, since no paper was detected within a specified period of time. In the event of such a situation, the user must follow the cumbersome procedure of opening the door of the copying machine, turning on a resetting switch to restore the jam detecting means, turning on the power supply switch, etc., although no paper jam has actually occurred.
Our copending U.S. application Ser. No. 254,275 filed on Apr. 15, 1981, discloses a copying apparatus including a manual paper feeding mechanism and a jam detecting mechanism which is so controlled to render the jam detecting mechanism in an inoperative condition when the paper is withdrawn after the manual paper feeding has commenced. U.S. Pat. No. 4,280,763 is cited of general interest to disclose a sequential control circuit for a copying machine.
The prior art is still seeking to optimize copier operation for the users.